In motor vehicle cruise control systems, a position controlled servo motor (pneumatic or electric) is mechanically coupled to the throttle of the vehicle engine to effect positioning of the throttle independent of a driver manipulated accelerator pedal. However, the linkage between the accelerator pedal and the throttle remains operative, enabling the driver to independently increase the throttle setting, overriding the throttle setting commanded by the cruise control system. Such an override is typically invoked when the driver wishes to temporarily accelerate the vehicle, to pass another vehicle, for example.
The vehicle powertrain control requirements often differ depending on whether the cruise control mode is engaged, since the primary objective of the cruise control is to maintain a steady vehicle speed. Certain transmission downshifting, for example, is typically inhibited or delayed during operation of the cruise control system.